The six noble gases are found in group 18 of the periodic
table. They are Helium, Neon, Argon, Krypton, Xenon, and Radon in order of
increasing atomic weight. These elements were considered to be inert gases, as
they have a closed-shell configuration, until
the 1960's, because their oxidation number of 0 prevents the noble gases from
forming compounds readily. This was found to be incorrect in 1962 when Neil
Bartlett succeeded in making the first complex xenon compound. His work was
confirmed by scientists at Argonne National Laboratory in
Illinois, who made the
first simple compound of Xenon and Fluorine (xenon tetrafluoride) and latter
made Radon and Krypton compounds. Although krypton compounds were made with
considerable difficulty, both xenon and radon reacted readily with fluorine, and
additional reactions to produce other compounds of xenon and radon could be
accomplished. All noble gases have the maximum number of electrons possible in
their outer shell (2 for Helium, 8 for all others), making them stable.

All of the Noble Gases are gases. The noble
gases are all found in minute quantities in the atmosphere, and are isolated by
fractional distillation of liquid air. Helium can be obtained from natural
gas
wells where it has accumulated as a result of
radioactive decay. All these gases
are monatomic. They boil at low temperatures as only dispersion forces act
between the atoms. Helium has the lowest boiling point of any substance at 4.2K.
The 1st ionization energy decreases on descending the Group, as the valence
shell becomes further away from the nucleus and electrons
become easier to remove. The
first ionization energy of xenon is comparable with that of bromine, which
explains why xenon forms compounds with oxygen and fluorine relatively easily.
The oxidation numbers of xenon in its compounds are +2, +4, +6 and +8. The Noble
Gases have important industrial functions. Click on the links to the individual
elements to find out more!

Krypton, Xenon, and Radon, being the heaviest inert gases, have been known to
form chemical combinations as stated before above. This is due to the forces between
the outermost electrons of these three elements and their
nuclei are diluted by
the distance and the interference of other electrons. The energy gained in
creating a Xenon or Radon Fluoride is greater than the energy required for
promotion of the reaction, and the compounds are chemically stable. Compounds of
Helium, Neon, or Argon, the electrons of which are more closely bound to their
nuclei, are unlikely to be created.